What I don'nt think you can do with the 37 (or 08) is haul passengers, while the 31 can only haul a 2-car 101. Perhaps this is something which should be addressed as it would make these locos far more suitable for WSR. 66s have also appeared at WSR galas in the past, so maybe they should be allowed to haul a rake of Mk1s (or Mk2s once NTP is released) as well. As I don't yet own the 20 I am unable to comment on it, although I am assuming that it is not able to haul passengers either.